1. Field of the Invention
The present invention relates to a controller of an internal combustion engine operable by an alcohol-containing fuel.
2. Description of the Related Art
Gasoline is used as a fuel in an internal combustion engine (engine) of an automobile or other vehicle. Meanwhile, there is a vehicle (FFV: Flexible Fuel Vehicle) in which is installed an engine enabled to use, in addition to gasoline, alcohol as an alternate fuel mixed at any ratio (0% to 100%).
The ratio of gasoline and alcohol (alcohol concentration; blend ratio) of a blended fuel supplied to an engine for FFV is not necessarily constantly fixed. For example, there may be a case where, in a state in which a blended fuel with an alcohol concentration of 80% is stored in a fuel tank of an FFV, a fuel of 0% alcohol concentration (that is, a fuel of 100% gasoline concentration) is supplied or a fuel of 100% alcohol concentration (that is, a fuel of 0% gasoline concentration) is supplied. Normally, the amount supplied also differs each time.
With an engine using a blended fuel, by ascertaining the alcohol concentration in the blended fuel, a fuel injection amount can be adjusted appropriately according to characteristics of the blended fuel. For example, although ethanol, which is an alcohol, is high in octane number, is thus less likely to cause knocking in comparison to alcohol, and has characteristics that are advantageous in terms of thermal efficiency, it is low in energy density, requires a fuel injection amount of 1.3 to 1.5 times that of gasoline, and thus has characteristics that are disadvantageous in terms of fuel consumption.
Due to such circumstances, for example, an art of enlarging a lean feedback region as the alcohol concentration increases and thereby improving the fuel consumption has been known (see JP-A-5-272383). However, from the point of traveling performance, there is a limit as to how much the lean feedback region can be enlarged, and because expansion of a lean operation region leads to early degradation of an exhaust purifying catalyst for cleaning an exhaust, the present circumstances are actually such that the lean operation region cannot be enlarged to a degree to which fuel consumption is improved adequately.
Thus, in actuality, with an engine for FFV, it is desired that improvement in exhaust gas performance by maintenance of exhaust purifying catalyst performance be achieved while achieving improvement in fuel consumption at the same time.